Dielectric and method for producing the same, and electrolytic capacitor

ABSTRACT

There are provided a dielectric and an electrolytic capacitor that have a small amount of leakage current, and have high reliability also in a high temperature environment. A dielectric containing at least zirconium, titanium, and a carbon atom, wherein a concentration of the carbon atom is 100 ppm or more and 10,000 ppm or less, and an atomic ratio of the titanium to a sum of the zirconium and the titanium is 30% or more and 90% or less.

This application is based upon and claims the benefit of priority from Japanese patent application No. 2014-88038, filed on Apr. 22, 2014, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a dielectric and a method for producing the same, and an electrolytic capacitor.

2. Description of the Related Art

An oxide containing a valve metal is mainly used for a dielectric forming the dielectric layer of an electrolytic capacitor. The oxide has valve action, has a high dielectric constant, and can achieve higher capacitance. Techniques related to dielectrics are disclosed in JP1-277342A, JP2010-34589A, JP43-18012B, JP6-333263A, JP9-165676A, JP2004-22702A, and JP2005-327428A.

However, in the techniques described in the above patent literatures, the amount of leakage current is large, and particularly in a high temperature environment, there is a tendency that the increase fluctuation of capacitance increases, and the leakage current increases, and therefore, the reliability is low.

It is an object of the present invention to provide a dielectric and an electrolytic capacitor that have a small amount of leakage current, and have high reliability also in a high temperature environment.

SUMMARY OF THE INVENTION

A dielectric according to the present invention is a dielectric containing at least zirconium, titanium, and a carbon atom, wherein a concentration of the carbon atom is 100 ppm or more and 10,000 ppm or less, and an atomic ratio of the titanium to a sum of the zirconium and the titanium is 30% or more and 90% or less.

A method for producing a dielectric according to the present invention includes mixing an alloy of zirconium and titanium with an organic binder to obtain a mixture; sintering the mixture to obtain a sintered body; and anodizing the sintered body.

A method for producing a dielectric according to the present invention includes heat-treating an alloy of zirconium and titanium in a gas containing organic compound A; and anodizing the alloy after the heat treatment.

A method for producing a dielectric according to the present invention includes anodizing an alloy of zirconium and titanium in a solution containing organic compound B.

An electrolytic capacitor according to the present invention includes the dielectric according to the present invention.

The present invention can provide a dielectric and an electrolytic capacitor that have a small amount of leakage current, and have high reliability also in a high temperature environment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Dielectric

A dielectric according to the present invention is a dielectric containing at least zirconium (Zr), titanium (Ti), and carbon atoms (C), wherein the concentration of the carbon atoms is 100 ppm or more and 10,000 ppm or less, and the atomic ratio of the titanium to the sum of the zirconium and the titanium (Ti/(Zr+Ti)) is 30% or more and 90% or less.

Ti has a relative dielectric constant exceeding those of Ta and Al, and therefore, its application to electrolytic capacitors is regarded as promising. However, an oxide that is a dielectric containing Ti is likely to crystallize, and therefore, a problem of the oxide is that the leakage current is likely to increase. Therefore, it is considered that a different element is added to Ti for alloying to suppress crystallization. However, for example, in a dielectric obtained using an alloy containing Ti and Zr, or Ti and Al, the leakage current is not sufficiently reduced, and the dielectric cannot be applied to an electrolytic capacitor. In addition, for the dielectric, in a high temperature environment, the increase fluctuation of capacitance increases, and the leakage current also increases because in a high temperature environment, oxygen atoms in the oxide that is the dielectric diffuse to the underlying valve metal side, and the effective thickness of the dielectric film decreases.

The dielectric according to the present invention contains zirconium, titanium, and carbon atoms at a particular ratio. In the present invention, the carbon atoms added in a slight amount can suppress the crystallization of the dielectric and stabilize the amorphous structure. Thus, a dielectric having a small amount of leakage current can be obtained. In addition, also in a high temperature environment, the carbon atoms added in a slight amount inhibit the movement of oxygen, and therefore, an increase in the increase fluctuation of capacitance and an increase in leakage current can be suppressed, and a dielectric having high reliability can be obtained. In this manner, the dielectric according to the present invention is useful as a dielectric for an electrolytic capacitor.

The concentration of carbon atoms in the dielectric according to the present invention is 100 ppm or more and 10,000 ppm or less. When the concentration of carbon atoms is less than 100 ppm, a sufficient crystallization suppression effect is not obtained, and the leakage current increases. On the other hand, when the concentration of carbon atoms exceeds 10,000 ppm, a carbide is formed to provide a dielectric having low insulating properties, and the leakage current increases. The concentration of carbon atoms is preferably 150 ppm or more and 8,000 ppm or less, more preferably 1,000 ppm or more and 7,000 ppm or less, and further preferably 2,000 ppm or more and 5,000 ppm or less. The measurement of the concentration of carbon atoms is carried out by a method described later. In addition, “ppm,” the unit of the concentration of carbon atoms, is a mass ratio.

The atomic ratio of the titanium to the sum of the zirconium and the titanium included in the dielectric according to the present invention is 30% or more and 90% or less. When the atomic ratio is less than 30%, the dielectric is a crystalline oxide and is not an amorphous structure. On the other hand, when the atomic ratio exceeds 90%, the dielectric changes from the amorphous structure to the crystalline oxide at low anodization voltage when the dielectric is produced by anodization described later. The atomic ratio is preferably 33% or more and 70% or less, more preferably 35% or more and 60% or less, and further preferably 37% or more and 50% or less. The measurement of the atomic ratio is carried out by a method described later.

The dielectric according to the present invention can be in a state in which carbon atoms are dissolved in an oxide containing zirconium and titanium. The state can be confirmed by XPS (X-ray photoelectron spectroscopy) and an EPMA (Electron probe micro analyzer).

The dielectric according to the present invention preferably includes an amorphous structure. When the dielectric includes an amorphous structure, the leakage current decreases. The fact that the dielectric includes an amorphous structure can be confirmed by a transmission electron microscope.

The dielectric according to the present invention may also contain a different element such as nitrogen atoms, fluorine atoms, or phosphorus atoms in addition to zirconium, titanium, and carbon atoms. Also when the dielectric contains the different element, the effects of the suppression of the crystallization of the dielectric and the inhibition of the diffusion of oxygen are obtained. The different element may be included in the dielectric at 10000 ppm or less and is preferably not included in the dielectric. The dielectric according to the present invention can contain oxygen atoms.

[Methods for Producing Dielectrics]

The dielectric according to the present invention can be preferably produced by embodiments shown below.

The concentration of carbon atoms in each of dielectrics obtained by methods according to the embodiments shown below is 100 ppm or more and 10,000 ppm or less. In a dielectric oxide film containing carbon atoms at the above concentration, the carbon atoms present dissolved in the film stabilize the amorphous structure of the oxide, and therefore, the leakage current is reduced. Further, in a high temperature environment, the carbon atoms present dissolved inhibit the diffusion of oxygen atoms in the dielectric oxide film into a metal layer that is a substrate, and therefore, an electrolytic capacitor having high reliability in which an increase in the increase fluctuation of capacitance and an increase in leakage current are suppressed is obtained. Also when no raw material for carbon atoms is intentionally added during dielectric fabrication, carbon atoms may be included as an impurity in zirconium and titanium at less than 100 ppm. However, the amount of the carbon atoms included as an impurity is small, and therefore, the concentration of carbon atoms in the dielectric is not 100 ppm or more unless a raw material for carbon atoms is intentionally added during dielectric fabrication.

In addition, the atomic ratio of titanium to the sum of zirconium and titanium in each of the dielectrics obtained by the above methods is 30% or more and 90% or less. When the atomic ratio is within the above range, a dielectric oxide film formed by anodization is likely to be an amorphous structure and is less likely to be a crystalline oxide. On the other hand, when the atomic ratio is outside the above range, a sufficient crystallization suppression effect of carbon atoms is not obtained, and an amorphous structure is not provided even if the dielectric contains carbon atoms at a concentration within the above range.

The dielectric according to the present invention is not limited to the dielectrics produced by the following embodiments.

First Embodiment

A method for producing a dielectric according to this embodiment includes mixing an alloy of zirconium and titanium with an organic binder to obtain a mixture; sintering the above mixture to obtain a sintered body; and anodizing the above sintered body. According to the method, an underlying metal in which carbon atoms are present dissolved is anodized, and therefore, the dielectric containing carbon atoms according to the present invention is easily obtained.

In the above method, first, an alloy of zirconium and titanium and an organic binder are mixed to obtain a mixture (hereinafter also shown as a mixing step). The atomic ratio of the zirconium to the titanium included in the alloy preferably satisfies the range of the atomic ratio of zirconium to titanium according to the present invention. As the alloy, for example, a powder of an alloy of zirconium and titanium can be used. As the organic binder, acrylic resins, polyvinyl alcohol resins, styrenic resins, camphor, and the like are preferred in terms of reactivity with the alloy of zirconium and titanium during sintering described later. These may be used singly or in combinations of two or more. Among these, acrylic resins are more preferred as the organic binder in terms of the strength of a pressure-press formed body. The organic binder contains carbon atoms and therefore is a raw material for the carbon atoms of the dielectric. For the mixing ratio of the above alloy to the above organic binder, when the amount of the above alloy is 100 parts by mass, the amount of the above organic binder is preferably 0.1 parts by mass or more and 40 parts by mass or less, more preferably 1 part by mass or more and 30 parts by mass or less, in terms of the suitable range of the amount of carbon atoms included in the dielectric. The method for mixing the above alloy and the above organic binder is not particularly limited, and they can be mixed using, for example, a blade type mixer. The fact that the zirconium and the titanium are alloyed can be confirmed by an X-ray diffraction method.

Next, the above mixture is sintered to obtain a sintered body (hereinafter also shown as a sintering step). In this step, most of the organic binder is gasified, but some carbon atoms in the organic binder react with the alloy of titanium and zirconium, and therefore, the alloy of titanium and zirconium containing a certain amount of carbon atoms is formed on the surface. In addition, when the above mixture is powdery, the obtained sintered body is porous. In terms of the suitable range of the amount of carbon atoms included in the dielectric, the sintering temperature is preferably 400° C. or more and 1200° C. or less, more preferably 500° C. or more and 1000° C. or less, and further preferably 600° C. or more and 800° C. or less. In addition, the sintering time is preferably 5 minutes or more and 3 hours or less, more preferably 15 minutes or more and 1 hour or less, and further preferably 20 minutes or more and 40 minutes or less. The sintering is preferably performed under reduced pressure, more preferably under vacuum.

Press forming the above mixture (hereinafter also shown as a press forming step) may be performed between the above mixing step and the above sintering step. For example, a press formed body can be fabricated by filling a die with the above mixture together with metal wire containing a valve metal, and pressure-press forming them. When the press forming step is performed, the obtained press formed body is sintered by the above sintering step to obtain a sintered body.

Next, the above sintered body is anodized. The anodization can be performed in a solution containing an electrolyte using the above sintered body as an anode. For this solution, aqueous solutions and nonaqueous solutions containing phosphoric acid, nitric acid, boric acid, citric acid, and sodium salts and ammonium salts thereof, and the like can be used. These may be used singly or in combinations of two or more. The concentration of the electrolyte in the solution can be 0.001% by mass or more and 80% by mass or less and is preferably 0.005% by mass or more and 1% by mass or less. The voltage of the anodization is preferably 1 V or more and 1000 V or less, more preferably 3 V or more and 500 V or less, and further preferably 50 V or more and 200 V or less. The temperature of the solution in performing anodization is preferably 0° C. or more and 100° C. or less, more preferably 15° C. or more and 95° C. or less, and further preferably 20° C. or more and 40° C. or less. By the anodization, the above sintered body is oxidized, and the dielectric according to the present invention is obtained.

Second Embodiment

A method for producing a dielectric according to this embodiment includes heat-treating an alloy of zirconium and titanium in a gas containing organic compound A; and anodizing the alloy after the above heat treatment. According to the method, an underlying metal in which carbon atoms are present dissolved is anodized, and therefore, the dielectric containing carbon atoms according to the present invention is easily obtained.

In the above method, first, an alloy of zirconium and titanium is heat-treated in a gas containing organic compound A. In this step, some of carbon atoms included in organic compound A are incorporated into the alloy of zirconium and titanium, and the alloy of titanium and zirconium containing a certain amount of carbon atoms is formed on the surface. The atomic ratio of the zirconium to the titanium included in the alloy of zirconium and titanium preferably satisfies the range of the atomic ratio of zirconium to titanium according to the present invention. As the alloy, for example, a plate of an alloy of zirconium and titanium can be used. The alloy plate can be fabricated by metallurgical processes such as rolling and casting and methods such as sputtering. The thickness of the alloy plate can be, for example, 100 nm to 1 mm. Examples of organic compound A include hydrocarbon gases such as methane, propane, ethylene, and acetylene. These may be used singly or in combinations of two or more. Among these, methane is preferred as organic compound A in terms of reactivity. When organic compound A is solid at the temperature of the heat treatment, organic compound A may be dissolved in an appropriate solvent and used as a liquid containing organic compound A.

Organic compound A may be diluted with an inert gas such as nitrogen or argon (Ar). In this case, in terms of the suitable range of the amount of carbon atoms included in the dielectric, preferably 0.01 mole % or more and 100 mole % or less, more preferably 0.1 mole % or more and 40 mole % or less, and further preferably 0.5 mole % or more and 10 mole % or less of organic compound A is included in the gas containing organic compound A.

In terms of the suitable range of the amount of carbon atoms included in the dielectric, the temperature of the heat treatment is preferably 400° C. or more and 1200° C. or less, more preferably 600° C. or more and 1000° C. or less, and further preferably 800° C. or more and 950° C. or less. In addition, the time of the heat treatment is preferably 1 minute or more and 3 hours or less, more preferably 15 minutes or more and 1 hour or less, and further preferably 20 minutes or more and 40 minutes or less.

Next, the alloy after the above heat treatment is anodized. The anodization can be performed as in the above first embodiment. By the anodization, the alloy after the above heat treatment is oxidized, and the dielectric according to the present invention is obtained.

Third Embodiment

A method for producing a dielectric according to this embodiment includes anodizing an alloy of zirconium and titanium in a solution containing organic compound B. According to the method, carbon is introduced into an underlying metal simultaneously with anodization, and therefore, the dielectric containing carbon atoms according to the present invention is easily obtained.

In the above method, an alloy of zirconium and titanium is anodized in a solution containing organic compound B. In this step, some of carbon atoms included in organic compound B are incorporated into the alloy of zirconium and titanium, and the alloy of titanium and zirconium containing a certain amount of carbon atoms is formed on the surface. As the alloy of zirconium and titanium, the same one as the alloy of zirconium and titanium in the above second embodiment can be used. Examples of organic compound B include organic solvents such as ethylene glycol, formamide, glycerin, and dimethyl sulfoxide. These may be used singly or in combinations of two or more. Among these, ethylene glycol is preferred as organic compound B in terms of safety and cost. The solution containing organic compound B can contain a solvent such as water or a nonaqueous solvent. In this case, in terms of the suitable range of the amount of carbon atoms included in the dielectric, preferably 0.01% by mass or more and less than 100% by mass, more preferably 0.1% by mass or more and 90% by mass or less, and further preferably 30% by mass or more and 70% by mass or less of organic compound B is included in the solution containing organic compound B.

The anodization can be performed in a solution containing the above organic compound B and an electrolyte using the above alloy of zirconium and titanium as an anode. As the electrolyte, phosphoric acid, nitric acid, boric acid, citric acid, and sodium salts and ammonium salts thereof, and the like can be used. These may be used singly or in combinations of two or more. The concentration of the electrolyte in the solution can be 0.001% by mass or more and 80% by mass or less and is preferably 0.005% by mass or more and 1% by mass or less. In terms of the suitable range of the amount of carbon atoms included in the dielectric, the voltage of the anodization is preferably 1 V or more and 1000 V or less, more preferably 3 V or more and 600 V or less, and further preferably 50 V or more and 200 V or less. In addition, the temperature of the solution in performing anodization is preferably 0° C. or more and 100° C. or less, more preferably 15° C. or more and 95° C. or less, and further preferably 20° C. or more and 40° C. or less. By the anodization, the above alloy of zirconium and titanium is oxidized incorporating carbon atoms, and the dielectric according to the present invention is obtained.

[Electrolytic Capacitor]

An electrolytic capacitor according to the present invention includes the dielectric according to the present invention. The electrolytic capacitor according to the present invention includes for a dielectric layer a dielectric in which the leakage current is low, and an increase in the increase fluctuation of capacitance and an increase in leakage current can be suppressed also in a high temperature environment, and therefore, the electrolytic capacitor has high reliability. For example, the configuration of the electrolytic capacitor according to the present invention is not particularly limited as long as it includes the dielectric according to the present invention for a dielectric layer. Known configurations can be adopted. Examples of the configuration include a configuration in which a cathode electrolyte such as manganese dioxide is formed on the dielectric according to the present invention, and a cathode layer including a graphite layer and a silver paste layer is further formed on the cathode electrolyte.

EXAMPLES

Examples of the present invention will be shown below, but the present invention is not limited to these.

[Concentration of Carbon Atoms]

The measurement of the concentration of carbon atoms included in a dielectric was carried out by a nondiffusive infrared absorption method. The measurement was carried out using CS-444LS (product name, manufactured by LECO).

[Atomic Ratio of Titanium to Sum of Zirconium and Titanium]

The number of moles of each of zirconium and titanium included in a dielectric was measured by an energy-dispersive X-ray analysis method. The measurement was carried out using Genesis 2000 (product name, manufactured by EDAX). Using the measurement results, the proportion of the number of moles of titanium to the sum of numbers of moles of zirconium and titanium was calculated to obtain the above atomic ratio.

[Leakage Current and Capacitance]

A dielectric obtained by anodization was washed with pure water, and a voltage of 70 V was applied to the dielectric in the same solution as during the anodization. Leakage current after 5 minutes from the start of the voltage application was measured (hereinafter shown as leakage current after anodization). In addition, capacitance was measured in a 5% by mass aqueous solution of ammonium borate at a frequency of 120 Hz (hereinafter shown as capacitance after anodization). Then, a high temperature storage test in which the dielectric was stored at 150° C. for 240 hours was performed. After the high temperature storage test, leakage current (hereinafter shown as leakage current after the high temperature storage test) and capacitance (hereinafter shown as capacitance after the high temperature storage test) were measured by the same methods as the above, respectively.

The rate of change of leakage current and the rate of change of capacitance were calculated by the following formulas.

(the rate of change of leakage current)=(leakage current after the high temperature storage test)/(leakage current after anodization)

(the rate of change of capacitance)=(capacitance after the high temperature storage test)/(capacitance after anodization)

In Table 1, leakage current after anodization is shown as a converted value when the value in Comparative Example 2 is 1.00.

Example 1

15 Parts by mass of an acrylic resin as an organic binder was added to 100 parts by mass of a powder of an alloy of titanium and zirconium (Ti:Zr=40:60 (atomic ratio)) to fabricate agglomerates of the alloy powder. A die was filled with the agglomerates together with metal wire containing an alloy of titanium and zirconium, and they were pressure-press formed to fabricate a press formed body having an outer shape of 2.2 mm×1.7 mm×1.2 mm. Next, the press formed body was sintered in a vacuum at a high temperature of 600° C. for 30 minutes to obtain a porous sintered body. At this time, most of the acrylic resin added as the organic binder was pyrolyzed and discharged as a gas, but the remainder reacted with the alloy powder and remained. 100 V anodization was performed in an aqueous solution containing phosphoric acid as an electrolyte at a concentration of 0.01% by mass at a liquid temperature of 25° C. using the porous sintered body as an anode to obtain a dielectric. The results are shown in Table 1.

Example 2

A plate of an alloy of titanium and zirconium (Ti:Zr=40:60 (atomic ratio), 20 mm long×10 mm wide×0.1 mm thick) was heat-treated in a mixed gas of methane and Ar (methane:Ar=1:99 (molar ratio)) at 900° C. for 30 minutes to react some of carbon atoms included in the methane with the alloy plate. Then, 100 V anodization was performed in an aqueous solution containing phosphoric acid as an electrolyte at a concentration of 0.01% by mass at a liquid temperature of 25° C. using the alloy plate as an anode to obtain a dielectric. The results are shown in Table 1.

Example 3

100 V anodization was performed in a solution containing phosphoric acid as an electrolyte at a concentration of 0.01% by mass and containing each of water and ethylene glycol as a solvent at a concentration of 50% by mass at a liquid temperature of 25° C. using a plate of an alloy of titanium and zirconium (Ti:Zr=40:60 (atomic ratio), 20 mm long×10 mm wide×0.1 mm thick) as an anode to obtain a dielectric. The results are shown in Table 1.

Example 4

100 V anodization was performed in a solution containing phosphoric acid as an electrolyte at a concentration of 0.01% by mass and containing each of water and ethylene glycol as a solvent at a concentration of 50% by mass at a liquid temperature of 25° C. using a plate of an alloy of titanium and zirconium (Ti:Zr=30:70 (atomic ratio), 20 mm long×10 mm wide×0.1 mm thick) as an anode to obtain a dielectric. The results are shown in Table 1.

Example 5

100 V anodization was performed in a solution containing phosphoric acid as an electrolyte at a concentration of 0.01% by mass and containing each of water and ethylene glycol as a solvent at a concentration of 50% by mass at a liquid temperature of 25° C. using a plate of an alloy of titanium and zirconium (Ti:Zr=90:10 (atomic ratio), 20 mm long×10 mm wide×0.1 mm thick) as an anode to obtain a dielectric. The results are shown in Table 1.

Example 6

A plate of an alloy of titanium and zirconium (Ti:Zr=40:60 (atomic ratio), 20 mm long×10 mm wide×0.1 mm thick) was heat-treated in a mixed gas of methane and Ar (methane:Ar=10:90 (molar ratio)) at 900° C. for 30 minutes to react some of carbon atoms included in the methane with the alloy plate. Then, 100 V anodization was performed in an aqueous solution containing phosphoric acid as an electrolyte at a concentration of 0.01% by mass at a liquid temperature of 25° C. using the alloy plate as an anode to obtain a dielectric. The results are shown in Table 1.

Example 7

1 Part by mass of a polyvinyl alcohol resin as an organic binder was added to 100 parts by mass of a powder of an alloy of titanium and zirconium (Ti:Zr=40:60 (atomic ratio)) to fabricate agglomerates of the alloy powder. A die was filled with the agglomerates together with metal wire containing an alloy of titanium and zirconium, and they were pressure-press formed to fabricate a press formed body having an outer shape of 2.2 mm×1.7 mm×1.2 mm. Next, the press formed body was sintered in a vacuum at a high temperature of 600° C. for 30 minutes to obtain a porous sintered body. At this time, most of the polyvinyl alcohol resin added as the organic binder was pyrolyzed and discharged as a gas, but the remainder reacted with the alloy powder and remained. 100 V anodization was performed in an aqueous solution containing phosphoric acid as an electrolyte at a concentration of 0.01% by mass at a liquid temperature of 25° C. using the porous sintered body as an anode to obtain a dielectric. The results are shown in Table 1.

Example 8

10 Parts by mass of a styrenic resin as an organic binder was added to 100 parts by mass of a powder of an alloy of titanium and zirconium (Ti:Zr=40:60 (atomic ratio)) to fabricate agglomerates of the alloy powder. A die was filled with the agglomerates together with metal wire containing an alloy of titanium and zirconium, and they were pressure-press formed to fabricate a press formed body having an outer shape of 2.2 mm×1.7 mm×1.2 mm. Next, the press formed body was sintered in a vacuum at a high temperature of 600° C. for 30 minutes to obtain a porous sintered body. At this time, most of the styrenic resin added as the organic binder was pyrolyzed and discharged as a gas, but the remainder reacted with the alloy powder and remained. 100 V anodization was performed in an aqueous solution containing phosphoric acid as an electrolyte at a concentration of 0.01% by mass at a liquid temperature of 25° C. using the porous sintered body as an anode to obtain a dielectric. The results are shown in Table 1.

Example 9

2 Parts by mass of camphor as an organic binder was added to 100 parts by mass of a powder of an alloy of titanium and zirconium (Ti:Zr=40:60 (atomic ratio)) to fabricate agglomerates of the alloy powder. A die was filled with the agglomerates together with metal wire containing an alloy of titanium and zirconium, and they were pressure-press formed to fabricate a press formed body having an outer shape of 2.2 mm×1.7 mm×1.2 mm. Next, the press formed body was sintered in a vacuum at a high temperature of 600° C. for 30 minutes to obtain a porous sintered body. At this time, most of the camphor added as the organic binder was pyrolyzed and discharged as a gas, but the remainder reacted with the alloy powder and remained. 100 V anodization was performed in an aqueous solution containing phosphoric acid as an electrolyte at a concentration of 0.01% by mass at a liquid temperature of 25° C. using the porous sintered body as an anode to obtain a dielectric. The results are shown in Table 1.

Comparative Example 1

A die was filled with a powder of an alloy of titanium and zirconium (Ti:Zr=40:60 (atomic ratio))together with metal wire containing an alloy of titanium and zirconium, and they were pressure-press formed to fabricate a press formed body having an outer shape of 2.2 mm×1.7 mm×1.2 mm. Then, a dielectric was fabricated as in Example 1 using the press formed body. The results are shown in Table 1.

Comparative Example 2

100 V anodization was performed in an aqueous solution containing phosphoric acid as an electrolyte at a concentration of 0.01% by mass at a liquid temperature of 25° C. using a plate of an alloy of titanium and zirconium (Ti:Zr=40:60 (atomic ratio), 20 mm long×10 mm wide×0.1 mm thick) as an anode to obtain a dielectric. The results are shown in Table 1.

Comparative Example 3

A dielectric was fabricated as in Example 3 except that a plate of an alloy of titanium and zirconium (Ti:Zr=20:80 (atomic ratio), 20 mm long×10 mm wide×0.1 mm thick) was used as the alloy plate. The results are shown in Table 1.

Comparative Example 4

A dielectric was fabricated as in Example 3 except that a zirconium plate (Ti:Zr=0:100 (atomic ratio), 20 mm long×10 mm wide×0.1 mm thick) was used instead of the alloy plate. The results are shown in Table 1.

Comparative Example 5

A plate of an alloy of titanium and zirconium (Ti:Zr=40:60 (atomic ratio), 20 mm long×10 mm wide×0.1 mm thick) was heat-treated in a mixed gas of methane and Ar (methane:Ar=50:50 (molar ratio)) at 900° C. for 30 minutes to react some of carbon atoms included in the methane with the alloy plate. Then, 100 V anodization was performed in an aqueous solution containing phosphoric acid as an electrolyte at a concentration of 0.01% by mass at a liquid temperature of 25° C. using the alloy plate as an anode to obtain a dielectric. The results are shown in Table 1.

Comparative Example 6

A dielectric was fabricated as in Example 3 except that a titanium plate (Ti:Zr=100:0 (atomic ratio), 20 mm long×10 mm wide×0.1 mm thick) was used instead of the alloy plate. The results are shown in Table 1.

TABLE 1 Leakage current after anodization Concen- (converted Rate of tration value with change Rate of Ti/ of carbon 1.00 in of change of (Zr + Ti) atoms Comparative leakage capaci- (%) (ppm) Example 2) current tance Example 1 40 4000 0.57 1.6 1.12 Example 2 40 2000 0.30 1.7 1.13 Example 3 40 3000 0.20 1.8 1.18 Example 4 30 3000 0.70 1.7 1.16 Example 5 90 3000 0.80 1.8 1.17 Example 6 40 9000 0.80 1.6 1.19 Example 7 40 5000 0.65 1.6 1.15 Example 8 40 8000 0.72 1.8 1.18 Example 9 40 4000 0.61 1.6 1.14 Comparative 40 70 1.00 2.6 1.47 Example 1 Comparative 40 50 1.00 3.3 1.53 Example 2 Comparative 20 3000 6.00 2.1 1.80 Example 3 Comparative 0 3000 7.00 2.2 1.90 Example 4 Comparative 40 15000 2.00 2.5 1.70 Example 5 Comparative 100 3000 12.00 2.4 1.80 Example 6 

What is claimed is:
 1. A dielectric comprising at least zirconium, titanium, and a carbon atom, wherein a concentration of the carbon atom is 100 ppm or more and 10,000 ppm or less, and an atomic ratio of the titanium to a sum of the zirconium and the titanium is 30% or more and 90% or less.
 2. A method for producing the dielectric according to claim 1, comprising: mixing an alloy of zirconium and titanium with an organic binder to obtain a mixture; sintering the mixture to obtain a sintered body; and anodizing the sintered body.
 3. The method for producing the dielectric according to claim 2, wherein the organic binder is at least one selected from the group consisting of an acrylic resin, a polyvinyl alcohol resin, a styrenic resin, and camphor.
 4. A method for producing the dielectric according to claim 1, comprising: heat-treating an alloy of zirconium and titanium in a gas comprising organic compound A; and anodizing the alloy after the heat treatment.
 5. A method for producing the dielectric according to claim 1, comprising: anodizing an alloy of zirconium and titanium in a solution comprising organic compound B.
 6. A dielectric produced by the method according to claim
 2. 7. A dielectric produced by the method according to claim
 3. 8. A dielectric produced by the method according to claim
 4. 9. A dielectric produced by the method according to claim
 5. 10. An electrolytic capacitor comprising the dielectric according to claim
 1. 11. An electrolytic capacitor comprising the dielectric according to claim
 6. 12. An electrolytic capacitor comprising the dielectric according to claim
 7. 13. An electrolytic capacitor comprising the dielectric according to claim
 8. 14. An electrolytic capacitor comprising the dielectric according to claim
 9. 